1. Technical Field
The present invention relates to a printing device and a recording paper conveyance mechanism.
2. Related Art
Holding recording paper to the platen surface that defines the printing position to the recording paper and thereby maintaining a highly precise platen gap is important in order to maintain good print quality in printers that print on recording paper by ejecting ink droplets from an ink ejection head. A suction platen that holds the recording paper to the platen surface by air suction while the paper is conveyed can be used to convey the recording paper while holding it tight to the platen surface. However, if the suction pressure is low, the recording paper may lift away from the platen surface and print quality drop, or the recording paper could rub against the ink ejection head and become soiled with ink.
To address this problem, Japanese Unexamined Patent Appl. Pub. JP-A-2010-201683 describes a printer having a first suction area that is divided into a grid and disposed substantially in the center of the platen width perpendicular to the recording paper conveyance direction with first suction holes formed in the bottom of each chamber of the grid in this first suction area, and second suction areas formed on opposite sides of the first suction area with second suction holes with a different arrangement or shape than the first suction holes in the first suction area. Relatively narrow recording paper is suctioned to the platen using the first suction area, and wide recording paper is suctioned to the platen using both the first suction area and second suction areas.
Japanese Unexamined Patent Appl. Pub. JP-A-2011-56694 describes a printer having a plurality of suction holes formed in the platen in both the recording paper conveyance and width directions, air chambers facing the suction holes, and suction means that pull air through the air chambers. There are two or more air chambers in the recording paper conveyance direction and a direction intersecting the conveyance direction. One suction means is connected to at least one air chamber, and at least one suction means is connected to another air chamber, and the printer changes the duty of the suction means in the area where the recording paper covers the suction holes, and the duty of the suction means in the area where all suction holes are not covered.
A problem with both JP-A-2010-201683 and JP-A-2011-56694 is that sufficient suction pressure cannot be achieved when narrow recording paper is used because the suction holes outside of the recording paper are open, air is pulled therethrough, and suction pressure is therefore lost. More particularly, print quality drops when relatively stiff recording paper is used because the recording paper lifts away from the platen, or the recording paper rubs against the ink ejection head and becomes soiled with ink.
A problem with JP-A-2011-56694 is that providing a suction means to the air chambers to be suctioned and also providing a suction means to the other air chambers is structurally complicated, and control is also complicated by changing the duty of plural suction means.